Kilograms

The kilogram is the base unit of mass in the International (SI) System of Units, and is accepted on a day-to-day basis as a unit of weight (the gravitational force acting on any given object).

The kilogram is almost exactly equal to the mass of one litre of water.

Definition:

The kg is defined as being equal to the mass of the International Prototype of the Kilogram (IPK), a block of platinum-iridium alloy manufactured in 1889 and stored at the International Bureau of Weights and Measures in Sèvres, France.

It is the only SI unit that is defined by a physical object rather than a fundamental physical property that can be reproduced in laboratories.

Origin:

For a short period the grave (also a metallic reference standard) was used to define one thousand grams, until it was replaced by the kilogram in 1799.

In 1795 metric measurement systems were introduced in France and the gram was defined as "the absolute weight of a volume of pure water equal to a cube of one hundredth of a metre, and at the temperature of the melting ice".

The kilogramme (derived from the Greek chilioi [thousand] and gramma [a small weight] was named as a more practical measure of mass for larger quantities in trade, and came to be used as the base unit of mass in all metric measurement systems.

The International (SI) System of Units published in 1960 used the kilogramme as the base unit of mass, and has been adopted by almost every country on earth (with a few notable the exceptions such as the United States).

Common references:

A kilogram is the approximate weight of a one litre bottle of soft drink.

Sugar is commonly sold in 1kg measures.

A typical basketball weighs approximately 1kg.

Usage context:

The kilogram is used globally on a day-to-day basis as a unit of measurement for mass and weight.

It is also the bass unit of mass for all m.k.s. measurement systems, where the metre, the kilogram and the second are used in relation to one another in order to define other concepts, such as the newton for force and the pascal as a measurement of pressure.

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